According to Grace Design, “noise from the computer USB port can cause jitter artifacts in the sensitive DAC circuits. To prevent this, the m9XX employs multi-tiered noise suppression. The first stage of noise suppression is provided by two high-quality USB cables, which are included with the m9XX. These high-speed cables feature RFI filters that are built-in, as well as extra-heavy 24AWG copper conductors for power and ground.”
USB power is also filtered at the input connectors on the rear panel. Power is separated into five individual supplies: one for the XMOS processor, one for the DAC, and three for the analog circuits. The audio amplifier power-supply rails are produced with an ultra-low-noise push-pull converter that runs synchronous to the digital audio clocks. This high-efficiency, low-noise power-supply circuit was originally designed for use in Grace’s Lunatec microphone preamplifiers, which have an EIN (equivalent input noise) of -130dB. This attention to noise suppression and isolation between digital and analog power yields a system with overall output noise of -109dBV A-weighted and-106dBV 22Hz–22kHz.
Setup and Ergonomics
The m9XX looks like no other DAC. Its extruded sheet-aluminum chassis is only 4¼" by 1" by 5" and features a large rotary knob on top. The front panel includes two ¼" stereo headphone jacks and a seven-section LED readout. The back panel has one pair of RCA line-out jacks, a TosLink input, a 5.0V 2A micro-B USB input, and a USB 2.0 input. That’s it. Because it has variable line-level outputs, the m9XX can serve as a DAC/preamplifier. The only drawback is that it only has one pair of outputs. If your system uses a subwoofer, you will need to connect it from either your amplifier’s high-level outputs or use a line-level splitter to supply an additional feed for your sub. I employed the latter methodology with no perceivable sonic ill effects.
I used the m9XX in two configurations—as a digital source with its output set at unity gain routed into a preamplifier, and as a DAC/pre, where it was connected directly to a power amplifier and the volume was controlled by the m9XX. In both situations the Grace m9XX performed without any issues. The only problem I encountered was user-error: One time I managed to switch from USB to TosLink via the menu, and I had to call Grace to discover my mistake (Alex, the customer service person, found the problem quickly and didn’t laugh at me).
Setting up the m9XX is simple, but because its display only supports two characters (due to its size restrictions), you will probably need to refer to Grace’s comprehensive and well-written user’s manual to determine what the display is trying to tell you. In USB 1 mode, the m9XX supports driverless operation on Mac OS and Windows at sample rates up to 96kHz. In Audio Class 2 mode, the m9XX supports driverless operation on Mac OS at sample rates up to 384kHz. On Windows, Audio Class 2 operation requires downloading and installing a free driver, available from Grace Design’s website.
Once the m9XX was hooked up, it was time to go into the set-up menu. Your first option will be whether to employ the cross-feed circuit. “CF” means the cross-feed is off while “C.F.” means the cross-feed is active. Next you can choose between the USB and TosLink inputs. “U” means USB while “To” means TosLink. Other set-up options include a dimmer control to lower the display brightness, a “power-up” option that lets you set the default volume level upon turn-on, the four digital filter options, and finally the USB mode. While it’s a bit scary at first, the menu is easily learnable and once you get the hang of it, going into and out of the m9XX’s set-up menu becomes quick and easy. And, yes, there’s no remote since the m9XX was envisioned as a “within hand’s reach” device.
Speaking of hands, the m9XX handles great “blind.” By that I mean after a day or so, once you’re through fiddling with the set-up menu, you can use the m9XX without ever having to look at it. The large top-mounted volume knob turns easily and the push-to-mute feature makes perfect sense. Another sensible feature is the way the two headphone outputs are slightly different—if you plug into the left one, the line-level output is unaffected, but if you plug into the right-hand one, the line-level output is muted.
Over the years I’ve spent time with a number of Grace Design DACs and A/Ds. And while there isn’t a pervasive “house sound” to Grace products, they do all share certain sonic attributes. The most important characteristic is a lack of listener fatigue during long sessions. I could listen to the m9XX for as many hours as I wanted (sometimes all day) and I never felt as if my ears needed a rest. But even with its easy-to-listen-to sound the m9XX was also as detailed and resolving as any DAC I’ve used. With my own recordings, which I know very well, the m9XX delivered all the low-level information and soundstaging cues that I’m accustomed to hearing. Part of the m9XX’s sonic appeal stems from its lucid character. This makes it easy to listen deep into a mix without any strain; all the aural information is simply there, clearly and without any loss of low-level details.
The m9XX’s harmonic balance is as neutral as I’ve heard from any DAC, which is surprising only if you also consider the m9XX’s excellent low-bass extension. Usually when a DAC has this much low-bass and sub-bass information its overall balance seems to shift toward “the dark side,” but the m9XX’s harmonic balance still sounds extremely neutral. Perhaps some of this apparent harmonic neutrality stems from the m9XX’s analog amplification section, which remains unfazed by dynamic peaks. This is a characteristic of Grace devices that J. Gordon Holt and I first discovered with our Lunatec microphone preamplifier. It was the first microphone preamplifier we had ever used whose sound did not change even when it was “hammered” by peak-level transients. I hear this same dynamically unflappable character with the m9XX.
Since one of the m9XX’s primary functions is to serve as a headphone amplifier, I connected more than a dozen different earphones of various types to try to find any mismatches. Beginning with the most sensitive in-ears I have, the Westone ES-5, I found the m9XX did have a slight amount of low-level hiss that was difficult to hear once music began playing. With the Westone ES-5, my usual listening levels were near the lower end of the m9XX’s output, between 20 and 30 (on a scale of 0 to 99). With Ultimate Ears’ newest custom in-ear, the In-Ear Reference Monitors Remastered, there was no hiss and normal listening levels were between 30 and 40. Moving over to the other extreme, the m9XX had no problems driving my least efficient and most power-hungry cans, the Beyerdynamic DT-990 600-ohm version, to what I consider loud levels while still having some power to spare, at a usual setting somewhere between 70 and 80.